[PATCH] md: Fixed refcounting/locking when attempting read error correction in raid10

We need to hold a reference to rdevs while reading and writing to attempt to
correct read errors.  This reference must be taken under an rcu lock.

Signed-off-by: Neil Brown <neilb@suse.de>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index ddc1dfc..1440935 100644 (file)
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1407,36 +1407,45 @@ static void raid10d(mddev_t *mddev)
                                if (s > (PAGE_SIZE>>9))
                                        s = PAGE_SIZE >> 9;
 
+                               rcu_read_lock();
                                do {
                                        int d = r10_bio->devs[sl].devnum;
-                                       rdev = conf->mirrors[d].rdev;
+                                       rdev = rcu_dereference(conf->mirrors[d].rdev);
                                        if (rdev &&
-                                           test_bit(In_sync, &rdev->flags) &&
-                                           sync_page_io(rdev->bdev,
-                                                        r10_bio->devs[sl].addr +
-                                                        sect + rdev->data_offset,
-                                                        s<<9,
-                                                        conf->tmppage, READ))
-                                               success = 1;
-                                       else {
-                                               sl++;
-                                               if (sl == conf->copies)
-                                                       sl = 0;
+                                           test_bit(In_sync, &rdev->flags)) {
+                                               atomic_inc(&rdev->nr_pending);
+                                               rcu_read_unlock();
+                                               success = sync_page_io(rdev->bdev,
+                                                                      r10_bio->devs[sl].addr +
+                                                                      sect + rdev->data_offset,
+                                                                      s<<9,
+                                                                      conf->tmppage, READ);
+                                               rdev_dec_pending(rdev, mddev);
+                                               rcu_read_lock();
+                                               if (success)
+                                                       break;
                                        }
+                                       sl++;
+                                       if (sl == conf->copies)
+                                               sl = 0;
                                } while (!success && sl != r10_bio->read_slot);
+                               rcu_read_unlock();
 
                                if (success) {
                                        int start = sl;
                                        /* write it back and re-read */
+                                       rcu_read_lock();
                                        while (sl != r10_bio->read_slot) {
                                                int d;
                                                if (sl==0)
                                                        sl = conf->copies;
                                                sl--;
                                                d = r10_bio->devs[sl].devnum;
-                                               rdev = conf->mirrors[d].rdev;
+                                               rdev = rcu_dereference(conf->mirrors[d].rdev);
                                                if (rdev &&
                                                    test_bit(In_sync, &rdev->flags)) {
+                                                       atomic_inc(&rdev->nr_pending);
+                                                       rcu_read_unlock();
                                                        atomic_add(s, &rdev->corrected_errors);
                                                        if (sync_page_io(rdev->bdev,
                                                                         r10_bio->devs[sl].addr +
@@ -1444,6 +1453,8 @@ static void raid10d(mddev_t *mddev)
                                                                         s<<9, conf->tmppage, WRITE) == 0)
                                                                /* Well, this device is dead */
                                                                md_error(mddev, rdev);
+                                                       rdev_dec_pending(rdev, mddev);
+                                                       rcu_read_lock();
                                                }
                                        }
                                        sl = start;
@@ -1453,17 +1464,22 @@ static void raid10d(mddev_t *mddev)
                                                        sl = conf->copies;
                                                sl--;
                                                d = r10_bio->devs[sl].devnum;
-                                               rdev = conf->mirrors[d].rdev;
+                                               rdev = rcu_dereference(conf->mirrors[d].rdev);
                                                if (rdev &&
                                                    test_bit(In_sync, &rdev->flags)) {
+                                                       atomic_inc(&rdev->nr_pending);
+                                                       rcu_read_unlock();
                                                        if (sync_page_io(rdev->bdev,
                                                                         r10_bio->devs[sl].addr +
                                                                         sect + rdev->data_offset,
                                                                         s<<9, conf->tmppage, READ) == 0)
                                                                /* Well, this device is dead */
                                                                md_error(mddev, rdev);
+                                                       rdev_dec_pending(rdev, mddev);
+                                                       rcu_read_lock();
                                                }
                                        }
+                                       rcu_read_unlock();
                                } else {
                                        /* Cannot read from anywhere -- bye bye array */
                                        md_error(mddev, conf->mirrors[r10_bio->devs[r10_bio->read_slot].devnum].rdev);